JP2003326367A - Method of producing pipe made of titanium for forming bellows - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the hardening of a pipe caused by a chemical change in titanium by using Ar and He as a shielding gas on plasma welding. <P>SOLUTION: In the method of producing a pipe made of titanium for forming bellows, hardening caused by the chemical change in titanium is prevented by using a gaseous mixture of argon and helium as a shielding gas on plasma welding in the production of a pipe stock (5). <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a bellows pipe made of titanium, and more particularly to a method for manufacturing a raw tube, which uses argon and hydrogen as shielding gases in plasma welding. The present invention relates to a new improvement for welding using a mixed gas of argon and helium without using a mixed gas of (1), reducing a decrease in convergence of a plasma arc, and preventing hardening due to a chemical change of titanium. 2. Description of the Related Art Conventionally, as a method of manufacturing this type of pipe for forming a bellows made of titanium, for example, a "method of manufacturing a titanium anticorrosion bellows" disclosed in Japanese Patent No. 2525960 is disclosed. In the method, a plate-shaped titanium material is formed into a cylindrical shape, and the opposite ends are welded to produce a raw tube, and the raw tube is bellowed by a hydraulic forming method or a roll forming method. In the method for producing a titanium bellows to be molded, the raw pipe is manufactured by using TI.
G welding is applied, and the thickness of the weld joint is 1.0
Bellows molding was to be performed at a rate of 5 times or more and 1.2 times or less, and with an Erichsen value after welding of 11.4 mm or more and 13.5 mm or less, which is equivalent to that of the base material. [0003] The conventional method of manufacturing a pipe for forming a bellows made of titanium has the following problems because it has been configured as described above. That is,
For vacuum bellows, plate thickness is 0.1 to 0.3m
A bellows is manufactured by manufacturing a pipe (base tube) from an ultrathin plate of m titanium. Welding of this ultra-thin plate requires a welding heat source that is stable with a small welding current.
It is very difficult with a welding machine, and plasma welding is used. However, in normal plasma welding, argon is used as the center gas (plasma gas) and a mixed gas of argon and hydrogen is used as the shielding gas. This is because the plasma arc column is converged by the thermal pinch effect due to the coupling, and a stable arc is obtained at a small current. Therefore, it is known that titanium reacts with hydrogen at high temperature and hardens, and in the welding of titanium, if hydrogen is present in the shielding gas, hardening and embrittlement of the molten metal part occurs,
Sound weld joints could not be obtained. Therefore, normal plasma welding cannot be applied, and if the welding speed is low, the heat input tends to be excessive, so that the hardness of the welded joint increases significantly and heat treatment is required for forming, which is also a vacuum heat treatment. Is required, and the manufacturing process is complicated, which has been an obstacle in mass production. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In particular, in manufacturing a raw tube, argon and helium are used without using a mixed gas of argon and hydrogen as a shielding gas in plasma welding. Using a mixed gas of
It is an object of the present invention to provide a method of manufacturing a pipe for forming a bellows made of titanium, in which a reduction in the degree of convergence of a plasma arc is reduced and welding is performed without causing hardening due to chemical change of titanium. A method for manufacturing a pipe for forming a bellows made of titanium according to the present invention is to form a plate-shaped titanium material into a cylindrical shape, and weld each of the opposing ends to form a raw tube. In the method of manufacturing a pipe for forming a bellows made of titanium, which is formed and bellows formed into a bellows by a hydroforming method or a roll forming method, a mixture of argon and helium is used as a shielding gas in plasma welding. This is a method using gas. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a method for manufacturing a titanium bellows pipe according to the present invention will be described below with reference to the drawings. FIG. 1 shows a bellows manufacturing process, in which a roll-shaped coil 2 of a titanium material 1 made of titanium and having a thickness of 0.2 mm is fed out and cut by a cutter to form a titanium plate 3. Each of the opposed ends 4a and 4b is welded by plasma welding to form a raw tube 5. Longitudinal welded portion 6 of this raw tube 5
After being checked, the bellows 8 is formed in a bellows shape by a hydraulic forming part 7 (which may be a roll forming method), and both end surfaces 8a and 8b of the bellows 8 are cut and removed to obtain the bellows 8. Can be After the bellows 8 has been degreased and washed, fittings 9a and 9b are attached to obtain a bellows product 10. As shown in FIG. 2, the raw tube 5 has a longitudinal welded portion 6 formed as a longitudinal welded joint 6A, and this longitudinal welded joint 6A is formed as shown in FIG. I have. That is, the thickness T of the longitudinal welded joint 6A
And it is configured to be substantially identical to the longitudinal weld thickness T _1. As shown in FIGS. 5 and 6, the bellows 8 can be changed in bellows by a formed bellows 8A and a bellows valley 8B, and is used for a vacuum gate valve, for example. [0009] The longitudinal welds 6 are formed by plasma welding, center gas used for the plasma welding using argon gas (Ar), as the shielding gas by using Ar + the He in place of the conventional Ar + H ₂ I have. EXAMPLE A pure titanium bellows having a thickness of 0.2 mm was manufactured. FIG. 1 shows the manufacturing process of the formed bellows. In the welding after the roll forming in the process (pipe welding),
Welding current 8 to 8.5 A, center gas: argon 0.3 L / min shielding gas: argon 10 L / min helium 0.2 to 0.5 L / min welding speed 900 mm / min To produce a pipe (bellows base pipe). Then, FIG.
According to the above process, hydroforming was performed to produce a sound bellows. The fatigue life of the manufactured bellows was confirmed to exceed the design value. In the case of a bellows formed using a welded pipe, if the longitudinal weld joint is unhealthy in the pipe expanding step during forming, the pipe will burst and cannot be expanded. The hardness of the molten metal in the longitudinal weld is significantly higher than that of the base metal (if the elongation is small), cracks occur from the heat-affected zone and break,
Bellows molding cannot be performed. (Conventionally, the structure of the molten metal part and the heat affected zone was changed by performing heat treatment,
Ensures ductility. The following test was conducted to confirm the effect of the helium mixed gas. When the mixed gas of the shielding gas was hydrogen and helium, the longitudinal joint of an ultrathin titanium plate was welded under the same welding conditions, and the hardness near the weld was measured. The results are shown in Tables 1 and 2 of Tables 1 and 2 and FIGS. Table 1 and FIG. 7 show the case where helium is mixed.
FIG. 8 shows the result when hydrogen was added. [Table 1] [Table 2] From these tables and figures, it can be seen that the average hardness (Vickers hardness) of the molten metal portion is clearly lower by about 10 when helium is mixed. From this, without causing hydrogen embrittlement and without performing heat treatment,
It is probable that a raw tube that could be formed was manufactured. Although it is possible to use only helium as the shielding gas, the helium gas is lighter than the atmosphere, so it is easy to get into the atmosphere, and the diffusion speed is high, so that the shielding effect is reduced and the melted part and the heat-affected zone are easily oxidized. Therefore, a mixed gas is most effective. A comparative test in TIG welding was also performed, but in the case of TIG, the welding speed was slow, so that the heat-affected zone was widened, and the hardness of the melted portion was almost the same as that in the case of the hydrogen-mixed shielding gas. [0014] The method for manufacturing a titanium bellows pipe according to the present invention is configured as described above.
The following effects can be obtained. In other words, the formation of the longitudinal welds forming the raw pipe is achieved by changing the shielding gas between Ar and H.
e, plasma welding is performed, so that a welded joint with a reduced increase in hardness at the welded portion can be obtained, and as a result, it is made of titanium with the same workability as a stainless steel bellows (high-speed welding, no heat treatment). Molded bellows can be manufactured, and the economic effect is extremely large.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a manufacturing process diagram showing a method for manufacturing a titanium bellows pipe according to the present invention. FIG. 2 is a side view showing the raw tube manufactured in FIG. FIG. 3 is a right side view of FIG. 1; FIG. 4 is an enlarged view showing a portion A in FIG. 3; FIG. 5 is an enlarged half sectional view showing the bellows of FIG. 1; FIG. 6 is a right side view of FIG. 5; FIG. 7 is a characteristic diagram showing a change in hardness of a longitudinal weld joint when a shielding gas according to the present invention is used. FIG. 8 is a characteristic diagram showing a change in hardness of a longitudinally welded joint portion when a conventional shielding gas is used. [Explanation of Signs] 1 Titanium material 4a, 4b End 5 Raw tube 8 Bellows

Claims (1)

Claims: 1. A plate-shaped titanium material (1) is formed into a cylindrical shape, and opposite ends (4a, 4b) are welded to produce a raw pipe (5). In a method for manufacturing a pipe for forming a bellows made of titanium by bellows forming a raw pipe (5) into a bellows (8) by a hydraulic forming method or a roll forming method, the raw material pipe (5) is used as a shielding gas in plasma welding. A method for producing a titanium bellows pipe, characterized by using a mixed gas of argon and helium.